While molding machines for insert molding using hot melt adhesives are known, these machines are typically adapted from hot melt application equipment. An example of such a system would be the OPTIMEL® 2000 (OPTIMEL is a registered trademark of Henkel) machine, available from OptiMel GmbH, Iserlohn, Germany. These systems have many disadvantages.
One disadvantage of machines based on hot melt adhesive application technology is that they typically use a heated hose to transport molten adhesive from a melt unit to an injection unit having an injection nozzle. The hoses must be heated or the adhesive will solidify in the hose. The use of such hoses is problematic due to the cost of replacing these hoses. In addition, the hoses often require frequent maintenance and replacement due to charring of the adhesive as it is transferred through the hose. The hoses limit both the molding materials that can be used and the temperature of the molding materials. It is typically not possible to heat the molding material to temperatures above the temperature achieved by the heated hose.
Systems using a heated hose are also disfavored because they do not allow precise control over the molding pressure. For instance, these molding machines operate around 100-1,000 psi. The molding pressure can generally only be controlled to about plus or minus 50 psi using known hot melt application based molding machines. Part of the reason for this imprecision is the large pressure loss between the pump/melt unit and the injection unit. The heated hoses used in these machines are often quite long (six feet, for example). The distance between the pump and the injection nozzle and the accompanying frictional forces require greater pump pressures to be used. This arrangement can cause a pressure differential between the pump and the injection nozzle.
High pressure injection molding is known. These systems typically are used to mold plastic materials. Examples of such machines are manufactured by Milacron Inc. of Cincinnati, Ohio. High pressure injection molding machines inject at pressures typically between 1,000 to 30,000 psi. These high pressures are unsuitable for over-molding certain components, such as electronics. In addition, many materials, including hot melt adhesives, are unsuitable for use in high pressure injection machines.
Epoxy potting has been used to encapsulate delicate components, such as electronics. However, epoxy based methods suffer from long curing times (24 hours) and large amounts of waste. Unused epoxy material will cure, rendering it useless for potting. Epoxy materials are also unsuitable for some applications because they tend to be very hard and brittle. Additionally, epoxy materials may be somewhat toxic and can be expensive.
U.S. application Ser. No. 10/202,433 (hereinafter, “the '433 application”) discloses an elegant solution to many of the problems of previous injection molding machines, hot melt application based machines, and epoxy methods. The '433 application discloses the use of a molding apparatus that operates at low pressures and allows for precise pressure control. The device allows even delicate electronic components to be molded.